It is known to apply pulverized protective substances to seed grains, whereby the grains are mixed with the protective substances in a mixing drum. This known method of application (seed-dressing) with pulverized substances has the disadvantage that due to abrasion, up to 50% of the protective substances are wasted, before the seeds are put in the ground. Because of this, it is necessary to apply overdoses in order to maintain the quantities necessary for the protection of the seeds in the soil. The overdosing has unfavorable effects on one hand on the health of the people involved in the seed-dressing operation and, on the other hand, on the environment,
By using seed dressings with liquid formulas, a slight improvement as to the strain on the operating personnel is achieved, but the excessive strain on the environment still persists, since the quantities are not reduced in order to insure a safe functioning. As long as preparations based on mercury were used for dressing of the seed grains, it was not necessary to provide a precise distribution of the protective substances over the surfaces of the seed grains, since these preparations produced a vapor stage, during which the seeds were permeated and the preparations could develop their full effectiveness.
Because of the replacement of the preparations based on mercury by other means which do not develop a vapor stage it became necessary to apply the seed dressing evenly, all around the surface of the seed grain.
The application of seed dressings in an even manner all over the surface of the seed grains is also a prerequisite for the reduction of the used quantities to the lowest possible level.
The attempt to use the known types of spraying equipment for the application of liquid seed dressings on the seed grains have failed due to the consistency of such seed dressings. Seed dressings with liquid formulas consist basically of a viscous carrier substance, wherein the active substance for seed dressing is dispersed. The usual spraying equipment becomes easily clogged due to the nature of the carrier substance, which has to insure the adherence of the seed dressing to the grain surface so that the equipment can become inoperable. They are therefore not suited for the application of liquid seed dressings.